Nickel electrode for alkali storage battery, method of producing nickel electrode for alkali storage battery, and alkali storage battery

ABSTRACT

A nickel electrode for an alkaline storage battery in which an active material mainly containing nickel hydroxide is applied to a porous sintered nickel substrate, wherein a layer containing at least one hydroxide of an element selected from a group consisting of Ca, Sr, Sc, Y, lanthanoid, and Bi is formed on a surface of the active material thus applied to the sintered nickel substrate, or between the sintered nickel substrate and the active material.

TECHNICAL FIELD

The present invention relates to a nickel electrode for an alkalinestorage battery in which an active material mainly containing nickelhydroxide is applied to a porous sintered nickel substrate, a method ofproducing the nickel electrode for an alkaline storage battery, and analkaline storage battery employing the nickel electrode as a positiveelectrode. The invention is characterized in that the improvement of thenickel electrode for an alkaline storage battery for suppressingself-discharge in a case where the alkaline storage battery in a chargedstate is stored at high temperatures, to improve storage characteristicsof the battery under high temperature conditions, and for sufficientlysuppressing oxygen evolution at the early stages in a case where thealkaline storage battery is charged under high temperature conditions,to improve charge characteristics of the battery under high temperatureconditions.

BACKGROUND ART

An alkaline storage battery such as a nickel-metal hydride battery ornickel-cadmium battery has conventionally employed a sintered nickelelectrode or a non-sintered nickel electrode as its positive electrode.

The non-sintered nickel electrode is produced by directly applying anactive material paste mainly containing nickel hydroxide to a conductiveporous body such as foamed nickel. Although it can be easily produced, adisadvantage exists that it is poor in charge-discharge characteristicsat high current.

On the other hand, the sintered nickel electrode employs a poroussintered nickel substrate obtained by sintering and is produced bychemically impregnating the porous sintered nickel substrate with a saltof the active material. The sintered nickel substrate presents higherconductivity. In addition, the electrode has excellent charge-dischargecharacteristics at high current because of good adhesion of the activematerial to the porous sintered nickel substrate. On this account, analkaline storage battery employing the sintered nickel electrode hasbeen favorably used in an electric power tool requiring high currentdischarge.

Unfortunately, however, the sintered nickel electrode has a lowerapplying ratio of the active material than the non-sintered nickelelectrode and therefor, must be improved in the utilization of theactive material. In addition, in an alkaline storage battery employingthe sintered nickel electrode, the above-mentioned sintered nickelsubstrate becomes weak due to the repeated charging and discharging ofthe battery. This results in low charge-discharge cycle characteristicsof the battery.

On this account, there has been conventionally proposed a sinterednickel electrode wherein a layer composed of cobalt hydroxide is formedon a surface of an active material applied to a porous sintered nickelsubstrate, after which the layer is heat-treated in the presence ofoxygen and an alkaline solution so that the cobalt hydroxide improve theconductivity of the active material thereby improving the utilizationthereof, as disclosed in JP, 1-200555, A. Also, there has been proposeda sintered nickel electrode wherein a layer composed of cobalt hydroxideis formed on a surface of a porous sintered nickel substrate, afterwhich the layer is heat-treated in the presence of oxygen and analkaline solution, and an active material mainly containing nickelhydroxide is then applied to the above-mentioned sintered nickelsubstrate, to inhibit the corrosion of the sintered nickel substrateduring the application of the active material so that charge-dischargecycle characteristics of the battery is improve, as disclosed in JP,63-216268, A.

Unfortunately, however, even in a case where the sintered nickelelectrode produced in the manner disclosed in the above-mentioned JP,1-200555, A is used as a positive electrode of an alkaline storagebattery, the alkaline storage battery still suffers the occurrence ofself discharge due to the oxygen evolution in the sintered nickelelectrode when the battery in a charged state is stored at a hightemperature of approximately 50° C. for a long time. Thus, the alkalinestorage battery is reduced in capacity.

Also, even in a case where the sintered nickel electrode produced in themanner as disclosed in the above-mentioned JP, 63-216268, A (JP,5-50099, B) is used as a positive electrode of an alkaline storagebattery, the oxygen evolution occurs in the alkaline storage batterycharged at a high temperature of approximately 50° C. before thepositive electrode is charged to full. As a result, the battery isdecreased in charge efficiency.

Further, there have been proposed a sintered nickel electrode wherein apositive-electrode active material contains yttrium hydroxide to improvethe utilization thereof under high temperature conditions as disclosedin JP, 48-50233, A, and a sintered nickel electrode wherein a compoundsuch as of yttrium, indium, antimony or the like is added to an activematerial mainly containing nickel hydroxide to improve the utilizationthereof under high temperature conditions as disclosed in JP, 5-28992,A.

However, in each of the sintered nickel electrodes disclosed in theseofficial gazettes, the compound such as of yttrium is simply added tothe active material. Therefore, the active material and the sinterednickel substrate are not sufficiently covered with the compound such asof yttrium. This detrimentally allows electrolyte solutions contact withthe active material and/or the sintered nickel substrate. Accordingly,oxygen evolution still occurs in the sintered nickel electrode underhigh temperature conditions, and sufficient increase in the utilizationof the active materials thus can not be achieved.

An object of the present invention is to provide, in an alkaline storagebattery employing as its positive electrode a sintered nickel electrodecomprising a porous sintered nickel substrate having an active materialmainly containing nickel hydroxide applied thereto, the alkaline storagebattery with excellent storage characteristics under high temperatureconditions by suppressing self-discharge due to the oxygen gas evolutionin the above-mentioned nickel electrode even when the battery in acharged state is stored at high temperature for a long time.

Another object of the invention is to provide, in an alkaline storagebattery employing as its positive electrode a sintered nickel electrodecomprising a porous sintered nickel substrate having an active materialmainly containing nickel hydroxide applied thereto, the alkaline storagebattery with a sufficient battery capacity under high temperatureconditions by suppressing oxygen evolution before the above-mentionednickel electrode is charged to full when the battery is charged underhigh temperature conditions.

DISCLOSURE OF INVENTION

A first nickel electrode for an alkaline storage battery according tothe present invention is a nickel electrode for an alkaline storagebattery comprising a porous sintered nickel substrate having an activematerial mainly containing nickel hydroxide applied thereto, wherein acoating layer containing at least one hydroxide of an element selectedfrom a group consisting of calcium Ca, strontium Sr, scandium Sc,yttrium Y, lanthanoid, and bismuth Bi is formed on a surface of theactive material thus applied to the porous sintered nickel substrate.

In producing the above-mentioned nickel electrode for an alkalinestorage battery, the active material mainly containing nickel hydroxideis applied to the porous sintered nickel substrate, after which thecoating layer containing at least one hydroxide of an element selectedfrom a group consisting of calcium Ca, strontium Sr, scandium Sc,yttrium Y, lanthanoid, and bismuth Bi is formed on the active materialthus applied to the porous sintered nickel substrate.

When an alkaline storage battery is produced using the above-mentionedfirst nickel electrode for an alkaline storage battery as its positiveelectrode, the above-mentioned coating layer formed on the surface ofthe active material applied to the porous sintered nickel substrateserves to prevent the active material and/or the sintered nickelsubstrate from coming into contact with an electrolyte solution.Therefore, even in a case where the alkaline storage battery in acharged state is stored at high temperatures, the above-mentionedcoating layer suppresses the oxygen gas evolution induced upon reactionof the electrolyte solution with the active material and the like,whereby storage characteristics of the battery under high temperatureconditions is improved.

Examples of a hydroxide of lanthanoid used in the above-mentionedcoating layer include a hydroxide of at least one element selected fromthe group consisting of lanthanum La, cerium Ce, praseodymium Pr,neodymium Nd, europium Eu, and ytterbium Yb.

Further, in the above-mentioned first nickel electrode for an alkalinestorage battery, it is preferable that cobalt is contained in theabove-mentioned hydroxide(s) in the coating layer. If an alkalinestorage battery employs the nickel electrode wherein cobalt is containedin the above-mentioned hydroxide(s) in the coating layer, the cobalt isoxidized to improve the conductivity of the nickel electrode, wherebythe alkaline storage battery is improved in the battery characteristics.

In forming the coating layer thus containing cobalt, when the coatinglayer is heat-treated in the presence of alkali and oxygen, theabove-mentioned cobalt is suitably oxidized by the heat treatment, tofurther improve the conductivity of the nickel electrode for an alkalinestorage battery. Further, unlike a case where cobalt iselectrochemically oxidized at the first time of charging with the nickelelectrode being used in an alkaline storage battery, the batterycapacity is not decreased. Furthermore, the cobalt thus oxidized furtherprevents the active material from being decomposed during the storage athigh temperatures, whereby the alkaline storage battery is furtherimproved in the storage characteristics under high temperatureconditions. In carrying out the heat treatment, when the temperature istoo low, the effects as described above can not be sufficientlyobtained. On the other hand, when the temperature is too high, theactive material applied to the sintered nickel substrate is decomposedand the sintered nickel substrate corrodes. Therefore, the temperatureof heat treatment is set preferably in the range of 60° C. to 100° C.

Further, in forming the coating layer using the above-mentionedhydroxide(s), when an amount of the above-mentioned hydroxide(s) is toosmall, the reaction between the electrolyte solution and the activematerial and the like can not be sufficiently suppressed on the otherhand, when an amount of the above-mentioned hydroxide(s) is too large, aratio of the active material applied to the nickel electrode for analkaline storage battery becomes low, whereby the battery cannot attaina sufficient battery capacity. Therefore, an amount of theabove-mentioned hydroxide(s) is set preferably in the range of 0.5 to 5wt % based on the total amount of all the applied materials whichinclude the active material mainly containing nickel hydroxide.

In the above-mentioned first nickel electrode for an alkaline storagebattery, it is preferred that zinc, cadmium, magnesium, cobalt,manganese, or the like is incorporated into the active material mainlycontaining nickel hydroxide as solid solution in order to prevent theexpansion of the nickel electrode during the charge/discharge processesof the battery.

A second nickel electrode for an alkaline storage battery according tothe present invention is a nickel electrode for an alkaline storagebattery comprising a porous sintered nickel substrate having an activematerial mainly containing nickel hydroxide applied thereto, wherein anintermediate layer containing at least one hydroxide of an elementselected from a group consisting of calcium Ca, strontium Sr, scandiumSc, yttrium Y, lanthanoid, and bismuth Bi is formed between the poroussintered nickel substrate and the active material.

In producing the above-mentioned nickel electrode for an alkalinestorage battery, the intermediate layer containing at least onehydroxide of an element selected from a group consisting of calcium Ca,strontium Sr, scandium Sc, yttrium Y, lanthanoid, and bismuth Bi isformed on the porous sintered nickel substrate, after which the activematerial mainly containing nickel hydroxide is applied to the poroussintered nickel substrate having the intermediate layer thus formedthereon.

When an alkaline storage battery employs the above-mentioned secondnickel electrode as its positive electrode, the intermediate layercontaining the above-mentioned hydroxides serves to prevent an oxygengas evolution potential from being lower along with the rise in thetemperature. Accordingly, when the alkaline storage battery is chargedunder high temperature conditions, oxygen gas is prevented form beinggenerated from the nickel electrode for an alkaline storage battery,resulting in improved charging efficiency of the battery under hightemperature conditions.

Examples of a hydroxide of lanthanoid used in the above-mentionedintermediate layer include a hydroxide of at least one element selectedfrom the group consisting of lanthanum La, cerium Ce, praseodymium Pr,neodymium Nd, europium Eu, and ytterbium Yb.

Further, in the above-mentioned second nickel electrode for an alkalinestorage battery, it is preferable that cobalt, together with theabove-mentioned hydroxide(s), is contained in the intermediate layer orthat a second intermediate layer composed of cobalt hydroxide is formedon the intermediate layer. If cobalt is contained in the intermediatelayer, or the second intermediate layer composed of cobalt hydroxide isformed on the intermediate layer, as respectively described above, thesintered nickel substrate is prevented form being corroded to beoxidized during the application of the above-mentioned active material.Moreover, when the nickel electrode for an alkaline storage battery isused in an alkaline storage battery, the cobalt contained in theintermediate layer or the cobalt hydroxide in the second intermediatelayer is oxidized to improve the conductivity of the nickel electrode,resulting in improved battery characteristics. Particularly, greatereffects are obtained in a case where the second intermediate layer isformed on the intermediate layer.

In forming the intermediate layer containing cobalt or forming thesecond intermediate layer composed of cobalt, hydroxide on theintermediate layer as respectively described above, when theintermediate layer or the second intermediate layer is heat-treated inthe presence of alkali and oxygen, the cobalt contained in theintermediate layer or the cobalt hydroxide in the second intermediatelayer is suitably oxidized by the heat treatment, to further improve theconductivity of the nickel electrode for an alkaline storage battery.Further, unlike a case where the cobalt contained in the intermediatelayer or the cobalt hydroxide in the second intermediate layer iselectrochemically oxidized at the first time of charging with the nickelelectrode for an alkaline storage battery being used in the alkalinestorage battery, the battery capacity is not decreased. In carrying outthe heat treatment, when the temperature is too low, the effects asdescribed above can not be sufficiently obtained. On the other hand,when the temperature is too high, the sintered nickel substratecorrodes. Therefore, the temperature of heat treatment is set preferablyin the range of 60° C. to 100° C.

Furthermore, in the second nickel electrode for an alkaline storagebattery, it is also preferred that zinc, cadmium, magnesium, cobalt,manganese, or the like is incorporated into the active material mainlycontaining nickel hydroxide as solid solution for the prevention of theexpansion of the nickel electrode during the charge/discharge processesof the battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing a state in which a coatinglayer composed of various hydroxides is formed on the active materialapplied to a porous sintered nickel substrate as in the presentexamples; and

FIG. 2 is a schematic sectional view showing a state in which anintermediate layer composed of various hydroxides is formed on a poroussintered nickel substrate, and an active material is then applied to thesintered nickel substrate having the intermediate layer thus formedthereon as in the present examples.

FIG. 3 is a schematic sectional view showing a state in which a secondintermediate layer is formed on the intermediate layer, between theintermediate layer and the coating layer.

MODE FOR CARRYING OUT THE INVENTION

A nickel electrode for an alkaline storage battery, a method ofproducing the nickel electrode for an alkaline storage battery, and analkaline storage battery according to examples of the present inventionwill be specifically described, and the excellent features thereof willbe clarified by comparison with comparative examples. The nickelelectrode for an alkaline storage battery, the method of producing thenickel electrode for an alkaline storage battery, and the alkalinestorage battery in the present invention are not particularly limited tothose described in the following examples, and can be embodied by beingsuitably changed within a range in which the gist thereof is notchanged.

EXAMPLES A1 TO A11

In the present examples, a porous sintered nickel substrate prepared inthe following manner was used to produce each nickel electrode for analkaline storage battery.

In preparation of the porous sintered nickel substrate, carbonyl nickelpowder and a binder was kneaded to adjust a nickel slurry, and theslurry was applied to a punching metal having a thickness of 50 μm. Theslurry on the punching metal was dried, and then sintered in a reducingatmosphere, to obtain the porous sintered nickel substrate. The poroussintered nickel substrate thus obtained had a porosity of approximately85% and a thickness of 0.65 mm.

Next, the porous sintered nickel substrate was immersed in a mixedsolution of nickel nitrate and cobalt nitrate (specific gravity: 1.75,atomic ratio between nickel and cobalt: 10:1) so that the mixed solutionwas impregnated into the porous sintered nickel substrate, after whichthe sintered nickel substrate was immersed in a 25% KOH aqueous solutionso that hydroxides of nickel and cobalt were deposited on the sinterednickel substrate. The above-mentioned operation was repeated 6 times, toapply an active material mainly containing nickel hydroxide to theabove-mentioned sintered nickel substrate.

Subsequently, Each coating layer 3 composed of a corresponding hydroxideshown in the following table 1 was formed on the active material 2mainly containing nickel hydroxide applied to the sintered nickelsubstrate 1, as shown in FIG. 1.

Aqueous solutions of 3 wt % nitrates were respectively prepared usingcalcium nitrate in the example A1; strontium nitrate in the example A2;scandium nitrate in the example A3; yttrium nitrate in the example A4;lanthanum nitrate in the example A5; cerium nitrate in the example A6;praseodymium nitrate in the example A7; neodymium nitrate in the exampleA8; europium nitrate in the example A9; ytterbium nitrate in the exampleA10; and bismuth nitrate in the example A11.

Each of the sintered nickel substrates having the active material mainlycontaining nickel hydroxide applied thereto was immersed in theabove-mentioned corresponding nitrate aqueous solution and then in a 25%NaOH aqueous solution at 80° C. to form each coating layer composed ofthe hydroxide of the above-mentioned corresponding element on theactive, material applied to the sintered nickel substrate. Each of thenickel electrodes for alkaline storage batteries was thus produced. Eachcoating layer of the above-mentioned each hydroxide formed on the activematerial in the above-mentioned manner had a constant weight per unitarea of 5 to 6 mg/cm². Further, an amount of the hydroxide in eachcoating layer was approximately 3 wt % based on the total amount of allthe applied materials which include the active material.

Further, when each of the active materials forming the coating layers asdescribed above was analyzed by an X-ray diffraction method, a peak ofthe hydroxide of the above-mentioned each element was observed inaddition to a peak of the nickel hydroxide. It was thus confirmed thatthe coating layer composed of the hydroxide of the above-mentioned eachelement was formed on the active material.

Although FIG. 1 is presented as a schematic sectional view of thepresent examples, it should be noted here that the active material 2mainly containing nickel hydroxide and the coating layer 3 composed ofthe hydroxide may be partially broken or may not be observed as atotally independent layer.

COMPARATIVE EXAMPLE a1

In the comparative example a1, a sintered nickel substrate having anactive material mainly containing nickel hydroxide applied thereto wasused as a nickel electrode for an alkaline storage battery as in theabove-mentioned examples A1 to A11, and a coating layer was not formedon the active material applied to the sintered nickel substrate.

COMPARATIVE EXAMPLE a2

In the comparative example a2, an active material mainly containingnickel hydroxide was applied to a porous sintered nickel substrate inthe same manner as that in the above-mentioned examples A1 to A11.Subsequently, the sintered nickel substrate was immersed in an aqueoussolution of 3 wt % cobalt nitrate and then in a NaOH aqueous solution sothat cobalt hydroxide was deposited on the active material applied tothe sintered nickel substrate. After that, the sintered nickel substratewetted with the NaOH aqueous solution was heat-treated in theatmosphere, that is in the presence of oxygen, at a temperature of 80°C. so that the above-mentioned cobalt hydroxide was oxidized. A nickelelectrode for an alkaline storage battery wherein a layer composed ofcobalt hydroxide was formed on the active material was thus produced. Itshould be noted here that the nickel electrode for an alkaline storagebattery thus produced is equivalent to the nickel electrode for analkaline storage battery disclosed in the above-mentioned JP, 1-200555,A.

COMPARATIVE EXAMPLE a3

In the comparative example a3, in applying an active material to aporous sintered nickel substrate obtained in the same manner as that inthe above-mentioned examples A1 to A11, a mixed aqueous solution ofnickel nitrate, cobalt nitrate, and yttrium nitrate (specific gravity:1.75, atomic ratio between nickel, cobalt, and yttrium: 10:1:0.81) wasused, and the sintered nickel substrate was immersed in the mixedaqueous solution so that the mixed solution was impregnated into theporous sintered nickel substrate. An active material mainly containingnickel hydroxide and additionally cobalt hydroxide and yttrium hydroxidewas then applied to the sintered nickel substrate in the same manner asthat in the above-mentioned examples A1 to A11 to produce a nickelelectrode for an alkaline storage battery. A coating layer was notformed on the active material applied to the sintered nickel substrate.

It should be noted here that the nickel electrode for an alkalinestorage battery thus produced is equivalent to the nickel electrode foran alkaline storage battery disclosed in the above-mentioned JP,48-50233, A.

Next, each of the nickel electrodes for alkaline storage batteries inthe above-mentioned examples A1 to A11 and comparative examples a1 to a3produced in the above-mentioned manner was used as a positive electrode,a hydrogen absorbing alloy electrode was used as a negative electrode,and a potassium hydroxide aqueous solution with normality 6 was used asa electrolyte solution to produced each alkaline storage battery havinga battery capacity of 1.0 Ah.

Each of the above-mentioned alkaline storage batteries was charged at acharging current of 100 mA for 16 hours, and then discharged at adischarge current of 200 mA to a battery voltage of 1.0 V. Theabove-mentioned charging and discharging were considered as one cycle.10 cycles of charging and discharging were performed at roomtemperature. After 11th cycle of charging was performed, each of theabove-mentioned alkaline storage batteries was committed to two-weekstorage at a temperature of 50° C. and thereafter, returned to place atroom temperature. Each of the above-mentioned alkaline storage batterieswas discharged to a battery voltage of 1.0 V to find a dischargingcapacity Q₁₁ at the 11th cycle time. The discharging capacity Q₁₁ at the11th cycle time was compared with a discharging capacity Q₁₀ at the 10thcycle time, which is before the storage, and the charge characteristicsunder high temperature conditions was calculated on the basis of thefollowing equation. The results are shown in the following Table 1.Storage characteristics (%)=(Q ₁₁ /Q ₁₀)×100

TABLE 1 Storage Materials of Characteristics Coating Layer (%) ExampleA1 Ca(OH)₂ 64 Example A2 Sr(OH)₂ 58 Example A3 Sc(OH)₃ 64 Example A4Y(OH)₃ 66 Example A5 La(OH)₃ 58 Example A6 Ce(OH)₃ 62 Example A7 Pr(OH)₃59 Example A8 Nd(OH)₃ 58 Example A9 Eu(OH)₃ 61  Example A10 Yb(OH)₃ 63 Example A11 Bi(OH)₃ 62 Comparative — 49 Example a1 Comparative Co(OH)₂54 Example a2 Comparative — 50 Example a3

As apparent from the results, the alkaline storage batteries in theexamples A1 to A11 employing the nickel electrodes for alkaline storagebatteries wherein the coating layers respectively composed of hydroxidesof Ca, Sr, Sc, Y, La, Ce, Pr, Nd, Eu, Yb, and Bi were formed on theactive materials mainly containing nickel hydroxides applied to thesintered nickel substrates were significantly improved in the storagecharacteristics under high temperature conditions, as compared with thealkaline storage battery in the comparative example a1 employing thenickel electrode for an alkaline storage battery wherein no coatinglayer was formed, the alkaline storage battery in the comparativeexample a2 employing the nickel electrode for an alkaline storagebattery wherein the coating layer composed of the heat-treated cobalthydroxide was formed, and the alkaline storage battery in thecomparative example a3 employing the nickel electrode for an alkalinestorage battery wherein cobalt hydroxide and yttrium hydroxide werecontained in the active material mainly containing nickel hydroxide.

EXAMPLES A4.1 to A4.9

In each of the examples A4.1 to A4.9, an active material mainlycontaining nickel hydroxide was applied to a sintered nickel substratein the same manner as that in the above-mentioned examples A1 to A11.Subsequently, in forming a coating layer on the active material thusapplied to the sintered nickel substrate, a nitrate aqueous solution ofyttrium was used to form a coating layer composed of yttrium hydroxideY(OH)₃, as in the above-mentioned example A4.

In the examples A4.1 to A4.9, the nitrate aqueous solutions of yttriumwere varied in the concentration (W1) of yttrium nitrate within therange of 0.1 to 7 wt % as shown in the following Table 2. Coating layerswere formed using such nitrate aqueous solutions of yttrium, to produceeach nickel electrode for an alkaline storage battery containing yttriumhydroxide in the weight percentage (W2) of 0.1 to 7 wt % based on thetotal amount of the yttrium hydroxide and the active material, as shownin the same table.

Each of the nickel electrodes for an alkaline storage batteries in theexamples A4.1 to A4.9 produced in the above-mentioned manner was used asa positive electrode to produce each alkaline storage battery having abattery capacity of 1.0 Ah in the same manner as that in theabove-mentioned examples A1 to A11. Discharge capacities Q₁₀ at the 10thcycle time and Q₁₁ at the 11th cycle time were measured to find storagecharacteristics under high temperature conditions. The results, alongwith that of the above-mentioned example A4, are shown in the followingTable 2.

TABLE 2 Storage Materials Character- of Coating W1 W2 Q₁₀ istics Layer(wt %) (wt %) (mAh/g) (%) Example A4.1 Y(OH)₃ 0.1 0.1 228 58 ExampleA4.2 Y(OH)₃ 0.3 0.3 230 60 Example A4.3 Y(OH)₃ 0.5 0.5 233 62 ExampleA4.4 Y(OH)₃ 1 1 235 64 Example A4.5 Y(OH)₃ 2 2 235 65 Example A4 Y(OH)₃3 3 235 66 Example A4.6 Y(OH)₃ 4 4 230 67 Example A4.7 Y(OH)₃ 5 5 228 68Example A4.8 Y(OH)₃ 6 6 223 68 Example A4.9 Y(OH)₃ 7 7 219 68

As apparent from the results, in forming the coating layer composed ofyttrium hydroxide on the active material applied to the sintered nickelsubstrate, when the yttrium hydroxide was contained in the weightpercentage of 0.5 to 5 wt % based on the total amount of the yttriumhydroxide and the active material, the battery was improved in thestorage characteristics under high temperature conditions and attainedthe high discharge capacity. Although the above-mentioned examples A4.1to A4.9 present a case where a coating layer composed of yttriumhydroxide was formed on the active material applied to the sinterednickel substrate, substantially the same results are obtained when acoating layer is composed of a hydroxide of element selected from thegroup consisting of calcium, strontium, scandium, lanthanoid, andbismuth.

EXAMPLES B1 TO B4

In each of the examples B1 to B4, an active material mainly containingnickel hydroxide was applied to a sintered nickel substrate in the samemanner as that in the above-mentioned examples A1 to A11.

In forming coating layers on the active materials thus applied to thesintered nickel substrates, there were used aqueous solutions of 3 wt %nitrate obtained by mixing calcium nitrate and strontium nitrate in theweight ratio of 1:1 in the example B1; calcium nitrate and cobaltnitrate in the weight ratio of 1:1 in the example B2; yttrium nitrateand cobalt nitrate in the weight ratio of 1:1 in the example B3; andbismuth nitrate and cobalt nitrate in the weight ratio of 1:1 in theexample B4.

Coating layer were formed on the active materials in the same manner asthat of the above-mentioned examples A1 to A11. As shown in thefollowing Table 3, there were formed coating layers respectivelycomposed of a mixture of Ca(OH)₂ and Sr(OH)₂ in the example B1; amixture of Ca(OH)₂ and Co(OH)₂ in the example B2; a mixture of Y(OH)₃and Co(OH)₂ in the example B3; and a mixture of Bi(OH)₃ and Co(OH)₂ inthe example B4, to obtain nickel electrodes for alkaline storagebatteries.

Each of the nickel electrodes for alkaline storage batteries in theexamples B1 to B4 produced in the above-mentioned manner was used as apositive electrode to produce each alkaline storage battery having abattery capacity of 1.0 Ah in the same manner as that in theabove-mentioned examples A1 to A11. Discharge capacities Q₁₀ at the 10thcycle time and Q₁₁ at the 11th cycle time were measured to find storagecharacteristics under high temperature conditions. The results, alongwith those of the above-mentioned examples A1, A4, and A11, are shown inthe following Table 3.

TABLE 3 Storage Materials of Characteristics Coating Layer (%) ExampleB1 Ca(OH)₂ + Sr(OH)₂ 66 Example B2 Ca(OH)₂ + Co(OH)₂ 69 Example B3Y(OH)₃ + Co(OH)₂ 72 Example B4 Bi(OH)₃ + Co(OH)₂ 70 Example A1 Ca(OH)₂64 Example A4 Y(OH)₃ 66 Example A11 Bi(OH)₃ 62

As apparent from the results, in forming the coating layer on the activematerial applied to the sintered nickel substrate, each of the alkalinestorage batteries in the examples B1 and B4 employing the nickelelectrode for an alkaline storage battery wherein the coating layercomposed of a mixture of two types of hydroxides was formed wereimproved in the storage characteristics under high temperatureconditions, as compared with the alkaline storage batteries in theexamples A1, A4, and A11 employing the nickel electrodes for alkalinestorage batteries wherein coating layers respectively composed of ahydroxide of calcium, yttrium, and bismuth were formed. Particularly,each of the alkaline storage batteries in the examples B2 and B4employing the nickel electrode for an alkaline storage battery whereinthe coating layer having a cobalt hydroxide mixed therein was formed wasfurther improved in the storage characteristics under high temperatureconditions. Although the examples B1 to B4 present a case where twotypes of hydroxides were mixed to form a coating layer, it should benoted here that more than two types of hydroxides may be mixed to form acoating layer.

EXAMPLES C1 TO C6

In each of the examples C1 to C6, an active material mainly containingnickel hydroxide was applied to a sintered nickel substrate in the samemanner as that in the above-mentioned examples A1 to A11. Subsequently,in forming coating layers on the active materials thus applied to thesintered nickel substrates, there were formed coating layers composed ofa mixture of Ca(OH)₂ and Co(OH)₂ in the example C1 as in theabove-mentioned example B2; Y(OH)₃ and Co(OH)₂ in the example C2 as inthe above-mentioned example B3; Bi(OH)₃ and Co(OH)₂ in the example C3 asin the above-mentioned example B4; Sc(OH)₃ and Co(OH)₂ in the example C4in the similar manner to that in the above-mentioned examples B1 to B4;La(OH)₃ and Co(OH)₂ in the example C5; and Yb(OH)₃ and Co(OH)₂ in theexample C6.

In the examples C1 to C6, in forming each coating layer as describedabove, each sintered nickel substrates having the active materialsapplied thereto was immersed in the above-mentioned correspondingnitrate aqueous solution and then in a NaOH aqueous solution so thateach hydroxide was deposited on the active material applied to thesintered nickel substrate. Subsequently, each of the sintered nickelsubstrates wetted with the NaOH aqueous solutions was heat-treated inthe atmosphere, that is in the presence of oxygen, at a temperature of80° C. so that cobalt hydroxide in the above-mentioned each hydroxidewas oxidized, to form each coating layer.

Each of the nickel electrodes for alkaline storage batteries in theexamples C1 to C6 produced in the above-mentioned manner was used as apositive electrode to produce each alkaline storage battery having abattery capacity of 1.0 Ah in the same manner as that in theabove-mentioned examples A1 to A11. Discharge capacities Q₁₀ at the 10thcycle time and Q₁₁, at the 11th cycle time were measured to find storagecharacteristics under high temperature conditions. The results, alongwith those of the above-mentioned examples B2 to B4, are shown in thefollowing Table 4.

TABLE 4 Storage Materials of Heat Characteristics Coating LayerTreatment (%) Example C1 Ca(OH)₂ + Co(OH)₂ yes 72 Example C2 Y(OH)₃ +Co(OH)₂ yes 77 Example C3 Bi(OH)₃ + Co(OH)₂ yes 75 Example C4 Sc(OH)₂ +Co(OH)₂ yes 76 Example C5 La(OH)₃ + Co(OH)₂ yes 72 Example C6 Yb(OH)₃ +Co(OH)₂ yes 74 Example B2 Ca(OH)₂ + Co(OH)₂ no 69 Example B3 Y(OH)₃ +Co(OH)₂ no 72 Example B4 Bi(OH)₃ + Co(OH)₂ no 70

As apparent from the results, in forming the coating layer on the activematerial applied to the sintered nickel substrate, the alkaline storagebatteries in the examples C1 to C6 employing the nickel electrodes foralkaline storage batteries wherein the coating layers respectivelycomposed of calcium hydroxide, yttrium hydroxide, bismuth hydroxide, andthe like mixed with cobalt hydroxides were formed on the activematerials applied to the sintered nickel substrates by the heattreatment in the presence of alkali and oxygen were further improved inthe storage characteristics under high temperature conditions, ascompared with the alkaline storage batteries in the examples B2 to B4employing the nickel electrodes for an alkaline storage batterieswherein the coating layers were formed without performing heattreatments.

EXAMPLES D1 TO D11

In the examples D1 to D11, porous sintered nickel substrates produced inthe same manner as that in the above-mentioned examples A1 to A11 wereused.

In the examples D1 to D11, each intermediate layer 4 composed of acorresponding hydroxide shown in the following Table 5 was formed on theabove-mentioned sintered nickel substrate 1, and an active material 3mainly containing nickel hydroxide was then applied to the sinterednickel substrate 1 thus having the intermediate layer 4 formed thereon,as shown in FIG. 2.

In forming each intermediate layer 4 composed of the correspondinghydroxide shown in the following Table 5, aqueous solutions of 10 wt %nitrates were respectively prepared using calcium nitrate in the exampleD1; strontium nitrate in the example D2; scandium nitrate in the exampleD3; yttrium nitrate in the example D4; lanthanum nitrate in the exampleD5; cerium nitrate in the example D6; praseodymium nitrate in theexample D7; neodymium nitrate in the example D8; europium nitrate in theexample D9; ytterbium nitrate in the example D10; and bismuth nitrate inthe example D11.

Then, each of the above-mentioned sintered nickel substrates wasimmersed in the above-mentioned corresponding nitrate aqueous solutionand then in a 25% NaOH aqueous solution at 80° C. to form thereon eachintermediate layer composed of the corresponding hydroxide shown in thefollowing Table 5. The presence of the above-mentioned intermediatelayer was confirmed by X-ray diffraction analysis. Each intermediatelayer of the above-mentioned corresponding hydroxide formed on thesintered nickel substrate in the above-mentioned manner had a constantweight per unit area of 8 to 10 mg/cm₂.

Next, in applying the active material mainly containing nickel hydroxideto each sintered nickel substrate thus having the intermediate layerformed thereon, each sintered nickel substrate was immersed in a mixedsolution of nickel nitrate and cobalt nitrate (specific gravity: 1.75,atomic ratio between nickel and cobalt: 10:1) so that the mixed solutionwas impregnated into the porous sintered nickel substrate, after whichthe sintered nickel substrate was immersed in a 25% NaOH aqueoussolution so that hydroxides of nickel and cobalt were deposited on thesintered nickel substrate. The same operation was repeated 6 times, toapply the active material mainly containing nickel hydroxide to theabove-mentioned sintered nickel substrate. Each of the nickel electrodesfor alkaline storage batteries was thus produced. An amount of thehydroxide in each intermediate layer was approximately 5 wt % based onthe total amount of the all the applied materials which include theactive material.

Although FIG. 2 is presented as a schematic sectional view of thepresent examples, it should be noted here that the intermediate layer 4composed of the hydroxide and the active material 3 mainly containingnickel hydroxide may be partially broken or may not be observed as atotally independent layer.

COMPARATIVE EXAMPLE d1

In the comparative example d1, a sintered nickel substrate having anactive material mainly containing nickel hydroxide applied thereto wasused as a nickel electrode for an alkaline storage battery as in theabove-mentioned comparative examples a1, and an intermediate layer wasnot formed on the sintered nickel substrate.

COMPARATIVE EXAMPLE d2

In the comparative example d2, a porous sintered nickel substrateproduced in the same manner as that in the above-mentioned examples A1to A11 was used. The sintered nickel substrate was then immersed in anaqueous solution of 3 wt % cobalt nitrate and then in a NaOH aqueoussolution so that cobalt hydroxide was deposited on the sintered nickelsubstrate. Subsequently, the sintered nickel substrate wetted with theNaOH aqueous solution was heat-treated in the atmosphere, that is in thepresence of oxygen, at a temperature of 80° C. so that cobalt hydroxidein the above-mentioned cobalt hydroxide was oxidized, to form anintermediate layer. After that, an active material mainly containingnickel hydroxide was applied to the sintered nickel substrate having theintermediate layer thus formed thereon to produce a nickel electrode foran alkaline storage battery as in the above-mentioned examples D1 toD11. It should be noted here that the nickel electrode for an alkalinestorage battery thus produced is equivalent to the nickel electrode foran alkaline storage battery disclosed in the above-mentioned JP,63-216268, A (JP, 5-50099, C).

Next, each of the nickel electrodes for alkaline storage batteries inthe above-mentioned examples D1 to D11 and comparative examples d1 andd2 produced in the above-mentioned manner was used as a positiveelectrode, a hydrogen absorbing alloy electrode was used as a negativeelectrode, and a potassium hydroxide aqueous solution with normality 6was used as a electrolyte solution to produce each alkaline storagebattery having a battery capacity of 1.0 Ah.

Each of the above-mentioned alkaline storage batteries was charged at acharging current of 100 mA for 16 hours, and then discharged at adischarge current of 200 mA to a battery voltage of 1.0 V. Theabove-mentioned charging and discharging were considered as one cycle.10 cycles of charging and discharging were performed at roomtemperature, after which 11th cycle of charging was performed at a hightemperature of 50° C. Subsequently, each of the above-mentioned alkalinestorage batteries was returned to place at room temperature so that eachof the above-mentioned alkaline storage batteries was discharged to abattery voltage of 1.0 V. A discharging capacity q₁₀ at the 10th cycletime and a discharging capacity q₁₁ at the 11th cycle time were comparedwith each other, and the charge characteristics under high temperatureconditions was calculated on the basis of the following equation. Theresults are shown in the following Table 5.Charge characteristics (%)=(q₁₁/q₁₀)×100

TABLE 5 Materials of Charge Intermediate characteristics Layer (%)Example D1 Ca(OH)₂ 72 Example D2 Sr(OH)₂ 68 Example D3 Sc(OH)₃ 73Example D4 Y(OH)₃ 77 Example D5 La(OH)₃ 68 Example D6 Ce(OH)₃ 70 ExampleD7 Pr(OH)₃ 70 Example D8 Nd(OH)₃ 71 Example D9 Eu(OH)₃ 73  Example D10Yb(OH)₃ 72  Example D11 Bi(OH)₃ 73 Comparative — 46 Example d1Comparative Co(OH)₂ 58 Example d2

As apparent from the results, the alkaline storage batteries in theexamples D1 and D11 employing the nickel electrodes for alkaline storagebatteries wherein the active material mainly containing nickel hydroxidewas applied to the sintered nickel substrate having the intermediatelayers respectively composed of hydroxides of Ca, Sr, Sc, Y, La, Ce, Pr,Nd, Eu, Yb, and Bi formed thereon were improved in the chargecharacteristics under high temperature conditions, as compared with thealkaline storage battery in the comparative example d1 employing thenickel electrode for an alkaline storage battery wherein no intermediatelayer was formed, and the alkaline storage battery in the comparativeexample d2 employing the nickel electrode for an alkaline storagebattery wherein the intermediate layer composed of heat-treated cobalthydroxide was formed. Further, in forming the intermediate layerscomposed of one hydroxide of element selected from the group consistingof Ca, Sr, Sc, Y, La, Ce, Pr, Nd, Eu, Yb, and Bi on the sintered nickelsubstrate, when the weight ratio of the hydroxide to the total amount ofthe hydroxide and the active material is set to the range of 0.5 to 5 wt%, the batteries are improved in charge characteristics under hightemperature conditions and attain large discharge capacities.

EXAMPLES E1 TO E3

In the examples E1 to E3, in forming intermediate layers on theabove-mentioned porous sintered nickel substrates, there were usedcalcium nitrate aqueous solution in the example E1 as in theabove-mentioned example D1; yttrium nitrate aqueous solution in theexample E2 as in the above-mentioned example D4; and bismuth nitrateaqueous solution in the example E3 as in the above-mentioned exampleD11.

In the examples E1 to E3, the sintered nickel substrates wererespectively immersed in the above-mentioned corresponding nitrateaqueous solutions, and then in 25% NaOH aqueous solutions, after whichthe sintered nickel substrates wetted with the NaOH aqueous solutionswere heat-treated in the atmosphere, that is in the presence of oxygen,at a temperature of 80° C. for one hour, to form intermediate layersrespectively composed of Ca(OH)₂, Y(OH)₃, and Bi(OH)₃ as shown in thefollowing Table 6. After that, each nickel electrode for an alkalinestorage battery was produced in the same manner as that in theabove-mentioned examples D1 to D11.

Each of the nickel electrodes for alkaline storage batteries in theexamples E1 to E3 produced as above was used as a positive electrode toproduce each alkaline storage battery having a battery capacity of 1.0Ah in the same manner as that in the above-mentioned examples D1 to D11.Also, discharge capacities q₁₀ at the 10th cycle time and q₁₁ at the11th cycle time were measured in the same manner as that in theabove-mentioned examples D1 to D11, to find charge characteristics underhigh temperature conditions. The results, along with those of theabove-mentioned examples D1, D4, and D11, are shown in the followingTable 6.

TABLE 6 Materials of Charge Intermediate Heat Characteristics LayerTreatment (%) Example E1 Ca(OH)₂ yes 74 Example E2 Y(OH)₃ yes 78 ExampleE3 Bi(OH)₃ yes 77 Example D1 Ca(OH)₂ no 72 Example D2 Y(OH)₃ no 77Example D3 Bi(OH)₃ no 73

As apparent from the results, the alkaline storage batteries in theexamples E1 to E3 employing the nickel electrodes for alkaline storagebatteries wherein heat treatments were performed in forming intermediatelayers respectively composed of hydroxides of calcium, yttrium, andbismuth were improved in the charge characteristics under hightemperature conditions, as compared with the alkaline storage batteriesin corresponding examples D1 to D3 employing the nickel electrodes foralkaline storage batteries wherein heat treatments were not performed informing the intermediate layers. In carrying out the heat treatment,when the temperature is too low, further improvement of the chargecharacteristics under high temperature conditions can not be achieved.On the other hand, if the temperature is too high, the sintered nickelsubstrate corrodes to degrade the battery characteristics. Therefore,the temperature of heat treatment is set preferably in the range of 60°C. to 100° C.

EXAMPLES F1 to F7

In the examples F1 to F7, in forming intermediate layers on theabove-mentioned porous sintered nickel substrates, there were usedaqueous solutions of 10 wt % nitrates respectively obtained by mixingcalcium nitrate and strontium nitrate in the weight ratio of 1:1 in theexample F1; calcium nitrate and cobalt nitrate in the weight ratio of1:1 in the example F2; scandium nitrate and cobalt nitrate in the weightratio of 1:1 in the example F3; yttrium nitrate and cobalt nitrate inthe weight ratio of 1:1 in the example F4; lanthanum nitrate and cobaltnitrate in the weight ratio of 1:1 in the example F5; ytterbium nitrateand cobalt nitrate in the weight ratio of 1:1 in the example F6; andbismuth nitrate and cobalt nitrate in the weight ratio of 1:1 in theexample F7.

Then, as in the above-mentioned examples E1 to E3, each of the sinterednickel substrates was immersed in the above-mentioned correspondingnitrate aqueous solution and then in a 25% NaOH aqueous solution, afterwhich the sintered nickel substrate wetted with the NaOH aqueoussolution was heat-treated in the atmosphere at a temperature of 80° C.for one hour. As shown in the following Table 7, there were formedintermediate layers respectively composed of a mixture of Ca(OH)₂ andSr(OH)₂ in the example F1; Ca(OH)₂ and Co(OH)₂ in the example F2;Sc(OH)₂ and Co(OH)₂ in the example F3; Y(OH)₃ and CO(OH)₂ in the exampleF4; La(OH)₃ and Co(OH)₂ in the example F5; Yb(OH)₃ and Co(OH)₂ in theexample F6; and Bi(OH)₃ and Co(OH)₂ in the example F7. After that, eachnickel electrode for an alkaline storage battery was produced in thesame manner as that in the above-mentioned examples D1 to D11.

Each of the nickel electrodes for alkaline storage batteries in theexamples F1 to F7 produced as above was used as a positive electrode,and each alkaline storage battery having a battery capacity of 1.0 Ahwas produced in the same manner as that in the above-mentioned examplesD1 to D11. Discharge capacities q₁₀ at the 10th cycle time and q₁₁ atthe 11th cycle time were measured to find charge characteristics underhigh temperature conditions. The results, along with those of theabove-mentioned examples E1 to E3, are shown in the following Table 7.

TABLE 7 Charge Materials of Heat Characteristics Intermediate LayerTreatment (%) Example F1 Ca(OH)₂ + Sr(OH)₂ yes 79 Example F2 Ca(OH)₂ +Co(OH)₂ yes 81 Example F3 Sc(OH)₃ + Co(OH)₂ yes 82 Example F4 Y(OH)₃ +Co(OH)₂ yes 87 Example F5 La(OH)₃ + Co(OH)₂ yes 82 Example F6 Yb(OH)₃ +Co(OH)₂ yes 85 Example F7 Bi(OH)₃ + Co(OH)₂ yes 86 Example E1 Ca(OH)₂yes 74 Example E2 Y(OH)₃ yes 78 Example E3 Bi(OH)₃ yes 77

As apparent from the results, each of the alkaline storage batteries inthe examples F1 to F7 employing the nickel electrode for an alkalinestorage battery wherein the above-mentioned two types of hydroxides wereheat-treated to form the intermediate layer was improved in the chargecharacteristics under high temperature conditions, as compared with eachof the alkaline storage battery in the examples E1 to E3 employing thenickel electrode for an alkaline storage battery wherein one type ofhydroxide of an element selected from the group consisting of calcium,yttrium, and bismuth was heat-treated to form the intermediate layer.Particularly, each of the alkaline storage batteries in the examples F2to F7 employing the nickel electrode for an alkaline storage batterywherein hydroxides including hydroxide of cobalt were heat-treated toform the intermediate layer was further improved in the chargecharacteristics under high temperature conditions. Further, in formingthe intermediate layer having cobalt hydroxide in addition to ahydroxide of calcium or the like, an amount of cobalt hydroxide was setpreferably in the range of 1 to 5 wt % based on the total amount of thehydroxide and the active material.

EXAMPLES G1 TO G6

In the examples G1 to G6, in forming intermediate layers on theabove-mentioned porous sintered nickel substrates, aqueous solutions of5 wt % nitrates were respectively prepared using calcium nitrate in theexample G1; scandium nitrate in the example G2; yttrium nitrate in theexample G3; lanthanum (La) nitrate in the example G4; ytterbium nitratein the example G5; and bismuth nitrate in the example G6. Then, theabove-mentioned sintered nickel substrates were immersed in theabove-mentioned corresponding nitrate aqueous solutions and then in 25%NaOH aqueous solutions at 80° C. to form the intermediate layersrespectively composed of Ca(OH)₂, Sc(OH)₃, Y(OH)₃, La(OH)₃, Yb(OH)₃, andBi(OH)₃ on the sintered nickel substrates.

Subsequently, each sintered nickel substrate having the intermediatelayer thus formed thereon was immersed in the aqueous solution of 5 wt %cobalt nitrate and then in a 25% NaOH aqueous solution, after which thesintered nickel substrate wetted with the NaOH aqueous solution washeat-treated in the atmosphere at a temperature of 80° C. for one hour,to form a second intermediate layer 4 a composed of a hydroxide ofcobalt on the above-mentioned intermediate layer 4 (see FIG. 3). Afterthat, each nickel electrode for an alkaline storage battery was producedin the same manner as that in the above-mentioned examples D1 to D11.

Each of the nickel electrodes for alkaline storage batteries in theexamples G1 to G6 produced as above was used as a positive electrode,and each alkaline storage battery having a battery capacity of 1.0 Ahwas produced in the same manner as that in the above-mentioned examplesD1 to D11. Discharge capacities q₁₀ at the 10th cycle time and q₁₁ atthe 11th cycle time were measured to find charge characteristics underhigh temperature conditions. The results, along with those of theabove-mentioned examples F2 to F7, are shown in the following Table 8.

TABLE 8 Charge Materials and State Characteristics of Intermediate layer(%) Example G1 Lamination of Ca(OH)₂ and Co(OH)₂ 87 Example G2Lamination of Sc(OH)₃ and Co(OH)₂ 89 Example G3 Lamination of Y(OH)₃ andCo(OH)₂ 90 Example G4 Lamination of La(OH)₃ and Co(OH)₂ 89 Example G5Lamination of Yb(OH)₃ and Co(OH)₂ 86 Example G6 Lamination of Bi(OH)₃and Co(OH)₂ 88 Example F2 Mixture of Ca(OH)₂ and Co(OH)₂ 81 Example F3Mixture of Sc(OH)₃ and Co(OH)₂ 82 Example F4 Mixture of Y(OH)₃ andCo(OH)₂ 87 Example F5 Mixture of La(OH)₃ and Co(OH)₂ 82 Example F6Mixture of Yb(OH)₃ and Co(OH)₂ 85 Example F7 Mixture of Bi(OH)₃ andCo(OH)₂ 86

As apparent from the results, each of the alkaline storage batteries inthe examples G1 to G7 employing the nickel electrode for an alkalinestorage battery wherein the intermediate layer composed of hydroxide ofcalcium or the like was formed on the sintered nickel substrate, and thesecond intermediate layer 4 a composed of the hydroxide of cobalt wasthen laminated on the intermediate layer 4 was further improved in thecharge characteristics under high temperature conditions, as comparedwith each of the alkaline storage batteries in the examples F2 to F7employing the nickel electrode for an alkaline storage battery whereinthe intermediate layer composed of the mixture of the hydroxide ofcalcium or the like and the hydroxide of cobalt was formed.

The above-mentioned examples only illustrates a case where a coatinglayer containing a hydroxide of calcium or the like is formed on asurface of an active material formed on a porous sintered nickelsubstrate and a case where an intermediate layer containing a hydroxideof calcium or the like is formed between a porous sintered nickelsubstrate and an active material. However, it is also possible to forman intermediate layer containing a hydroxide of calcium or the likebetween a porous sintered nickel substrate and an active material alongwith forming a coating layer containing a hydroxide of calcium or thelike on a surface of the active material thus formed on the sinterednickel substrate.

INDUSTRIAL APPLICABILITY

As described in detail above, in the first nickel electrode for analkaline storage battery according to the present invention, a coatinglayer containing at least one hydroxide of an element selected from agroup consisting of calcium Ca, strontium Sr, scandium Sc, yttrium Y,lanthanoid, and bismuth Bi is formed on a surface of an active materialapplied to a porous sintered nickel substrate. Therefore, when analkaline storage battery is produced using the first nickel electrodefor an alkaline storage battery according to the present invention as apositive electrode, the above-mentioned coating layer serves to preventthe active material and/or the sintered nickel substrate from contactingwith an electrolyte solution. Accordingly, even in a case where thealkaline storage battery in a charged state is stored under hightemperature conditions, the above-mentioned coating layer inhibits theoxygen gas evolution induced upon reaction of the electrolyte solutionwith the active material and the like, whereby the alkaline storagebattery with excellent storage characteristics under high temperatureconditions is obtained.

Further, in the second nickel electrode for an alkaline storagebatteries according to the present invention, an intermediate layercontaining at least one hydroxide of an element selected from a groupconsisting of calcium Ca, strontium Sr, scandium Sc, yttrium Y,lanthanoid, and bismuth Bi is formed between a porous sintered nickelsubstrate and an active material.

Therefore, when an alkaline storage battery is produced using the secondnickel electrode for an alkaline storage battery according to thepresent invention as a positive electrode, the intermediate layercontaining the above-mentioned hydroxide(s) serves to prevent an oxygengas evolution potential from being lower along with the rise in thetemperature. Therefore, when the alkaline storage battery is chargedunder high temperature conditions, oxygen gas is prevented form beinggenerated from the nickel electrode for an alkaline storage battery,whereby the alkaline storage battery with excellent chargecharacteristics under high temperature conditions is obtained.

1. A sintered nickel electrode for an alkaline storage battery in whichan intermediate layer of an active material mainly containing nickelhydroxide is applied to a porous sintered nickel substrate,characterized in that a coating layer consisting of at least onehydroxide of an element selected from the group consisting of strontiumSr, scandium Sc, yttrium Y, the lanthanoid elements, and bismuth Bi isformed on a surface of the intermediate layer opposite the poroussintered nickel substrate.
 2. The sintered nickel electrode for analkaline storage battery according to claim 1, characterized in thatsaid lanthanoid is at least one element selected from the groupconsisting of lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd,europium Eu, and ytterbium Yb.
 3. The sintered nicked electrode for analkaline storage battery according to claim 1, characterized in that anamount of said hydroxide in the coating layer is in the range of 0.5 to5 wt % based on the total amount of all the applied materials whichincludes the active material mainly containing nickel hydroxide.
 4. Analkaline storage battery characterized in that the sintered nickelelectrode for an alkaline storage battery according to claim 1 is usedas its positive electrode.
 5. A sintered nickel electrode for analkaline storage battery in which an intermediate layer of an activematerial mainly containing nickel hydroxide is applied to a poroussintered nickel substrate, characterized in that a coating layercontaining cobalt together with at least one hydroxide of an elementselected from the group consisting of calcium Ca, strontium Sr, scandiumSc, yttrium Y, the lanthanoid elements, and bismuth Bi is formed on asurface of the intermediate layer opposite the porous sintered nickelsubstrate.
 6. The sintered nickel electrode for an alkaline storagebattery according to claim 5, characterized in that said coating layercontaining cobalt is heat-treated in the presence of alkali and oxygen.7. An alkaline storage battery characterized in that the sintered nickelelectrode for an alkaline storage battery according to claim 5 is usedas its positive electrode.